1. Field of the Invention
The invention relates to communication method.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. A session may, for example, be a telephone call between users or multi-way conference session, or a communication session between user equipment and an application server (AS), for example a service provider server. The establishment of these sessions generally enables a user to be provided with various services.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable communication by means of the system.
Communication systems providing wireless communication for user equipment are known. An example of the wireless systems is the public land mobile network (PLMN). The PLMNs are typically based on cellular technology. In cellular systems, a base transceiver station (BTS) or similar access entity serves wireless user equipment (UE) known also as mobile stations (MS) via a wireless interface between these entities. The communication on the wireless interface between the user equipment and the elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected.
One or more gateway nodes may also be provided for connecting the cellular network to other networks e.g. to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks. In such arrangement the mobile communications network provides an access network enabling a user with a wireless user equipment to access external networks, hosts, or services offered by specific service providers. The access point or gateway node of the mobile communication network then provides further access to an external network or an external host. For example, if the requested service is provided by a service provider located in other network, the service request is routed via the gateway to the service provider. The routing may be based on definitions in the mobile subscriber data stored by a mobile network operator.
An example of the services that may be offered for user such as the subscribers to a communication systems is the so called multimedia services. Some of the communication systems enabled to offer multimedia services are known as Internet Protocol (IP) Multimedia networks. IP Multimedia (IM) functionalities can be provided by means of an IP Multimedia Core Network (CN) subsystem, or briefly IP Multimedia subsystem (IMS). The IMS includes various network entities for the provision of the multimedia services. The IMS services are intended to offer, among other services, IP connections between mobile user equipment.
The third generation partnership project (3GPP) has defined use of the general packet radio service (GPRS) for the provision of the IMS services, and therefore this will be used in the following as an example of a possible backbone communication network enabling the IMS services. The exemplifying general packet radio service (GPRS) operation environment comprises one or more sub-network service areas, which are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes (SN). In this application the service nodes will be referred to as serving GPRS support nodes (SGSN). Each of the SGSNs is connected to at least one mobile communication network, typically to base station systems. The connection is typically by way of radio network controllers (RNC) or other access system controllers such as base stations controllers (BSC) in such a way that packet service can be provided for mobile user equipment via several base stations. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile user equipment. Different sub-networks are in turn connected to an external data network, e.g. to a public switched data network (PSPDN), via gateway GPRS support nodes (GGSN). The GPRS services thus allow packet data transmission between mobile data terminals and external data networks.
In such a network, a packet data session is established to carry traffic flows over the network. Such a packet data session is often referred as a packet data protocol (PDP) context. A PDP context may include a radio access bearer provided between the user equipment, the radio network controller and the SGSN, and switched packet data channels provided between the serving GPRS support node and the gateway GPRS support node.
A data communication session between the user equipment and other party would then be carried on the established PDP context. Each PDP context can carry more than one traffic flow, but all traffic flows within one particular PDP context are treated the same way as regards their transmission across the network. The PDP context treatment requirement is based on PDP context treatment attributes associated with the traffic flows, for example quality of service and/or charging attributes.
The Third Generation Partnership Project (3GPP) has also defined a reference architecture for the third generation (3G) core network which will provide the users of user equipment with access to the multimedia services. This core network is divided into three principal domains. These are the Circuit Switched (CS) domain, the Packet Switched (PS) domain and the Internet Protocol Multimedia (IM) domain. The latter of these, the IM domain, is for ensuring that multimedia services are adequately managed.
The IM domain supports the Session Initiation Protocol (SIP) as developed by the Internet Engineering Task Force (IETF). Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying and terminating sessions with one or more participants (endpoints). SIP was generally developed to allow for initiating a session between two or more endpoints in the Internet by making these endpoints aware of the session semantics. A user connected to a SIP based communication system may communicate with various entities of the communication system based on standardised SIP messages. User equipment or users that run certain applications on the user equipment are registered with the SIP backbone so that an invitation to a particular session can be correctly delivered to these endpoints. To achieve this, SIP provides a registration mechanism for devices and users, and it applies mechanisms such as location servers and registrars to route the session invitations appropriately. Examples of the possible sessions that may be provided by means of SIP signalling include Internet multimedia conferences, Internet telephone calls, and multimedia distribution.
Reference is made to IETF document RFC 3325 which is hereby incorporated by reference. This document describes private extensions to SIP that enable a network of trusted SIP servers to assert the identity of end users or end systems, and to convey indications of end-user requested privacy. The use of these extensions is applicable inside a ‘Trust Domain’ as defined in Short term requirements for Network Asserted Identity. Nodes in such a Trust Domain are explicitly trusted by its users and end-systems to publicly assert the identity of each party, and to be responsible for withholding that identity outside of the Trust Domain when privacy is requested.
In order to be able to apply the privacy procedures described in RFC3325, there is a need to detect the trustworthiness of the next hop network. If the next hop is trusted, then the procedures related to the different privacy options are delegated to the next hop. Otherwise the privacy procedures need to be executed.
As an example, in case the caller asks for identity privacy, the P-Asserted-Identity header has to be removed before it reaches the called party. A message sent by the caller contains a header identifying the sender, called a P-Asserted-Identity header. The format of this header if the sender is a user with a publicly-known user identification is: <sip:user1_public1@home1.net> The home network of the caller has to remove the header only in case the home network of the called party is not trusted. If the home network of the called party (which is the next hop for the home network of the caller) is trusted, then the home network of the caller will not remove the header. This is needed to be compliant with RFC3325, which says that the P-Asserted-Identity header has to be removed by the last element in the trusted domain.
In RFC 3325, the mechanism proposed relies on the header field called ‘P-Asserted-Identity’ that contains a URI (commonly a SIP URI) and an optional display-name. A proxy server which handles a message can, after authenticating the originating user in some way (for example: Digest authentication), insert such a P-Asserted-Identity header field into the message and forward it to other trusted proxies. A proxy that is about to forward a message to a proxy server or UA that it does not trust removes all the P-Asserted-Identity header field values if the user requested that this information be kept private. Users can request this type of privacy.
For the procedures to be applied in the correct place, the trustworthiness of the next hop has to be detected in some way.